High-Ionic-Strength wastewater treatment via catalytic wet oxidation over a MnCeOx catalyst

Catalytic wastewater treatment has rarely been applied to treat high-ionic-strength wastewater (HISWW) as it contains large amounts of catalyst poisons (e.g., Cl–). This work investigates the catalytic wet oxidation (CWO) of phenol over a MnCeOx catalyst in the presence of high NaCl concentrations where the combination of MnCeOx and NaCl promoted the CWO of phenol. Specifically, in the presence of NaCl at a concentration of 200 g L–1 and MnCeOx at a concentration of 1.0 g L–1, phenol (initially 1.0 g L–1) and total organic carbon (TOC) conversions were ∼98 and 85%, respectively, after a 24 h reaction. Conversely, under the same reaction conditions without NaCl, the catalytic system only achieved phenol and TOC conversions of ∼41 and 27%, respectively. In situ Attenuated Total Reflection infrared spectroscopy identified the nature of the strongly adsorbed carbon deposits with quinone/acid species found on Ce sites and phenolate species on Mn sites in the single oxides and on MnCeOx. The presence of high concentrations of NaCl reduced the carbon deposition over the catalyst, promoting surface oxidation of the hydrocarbon and reoxidation of the catalyst, resulting in enhanced mineralization. Moreover, the used MnCeOx catalyst in the salt water system was efficiently regenerated via a salt water wash under the reaction conditions, showing the great potential of MnCeOx in practical HISWW treatment.